This project will explore the relationship between central noradrenergic (NA) function and reading disabilities (RD) in children with ADHD. This study will determine whether alpha-2 receptors in the brain are involved in the pathophysiology of ADHD, and whether the difference in NA function between RD and non-RD subgroups of ADHD children, as indicated by baseline MHPG levels, is due to a difference in central alpha-2 function.